This invention relates to fulcrum devices as used in automatic screw machines and more particularly to an improved means for pivotally mounting the opposed chuck levers of such fulcrum devices. Such fulcrum devices have a pair of pivotal chuck levers which control a collet chuck for engaging lengths of rod or pipe as they are fed into an automatic screw machine.
Automatic screw machines which are well known in the prior patented art have a hollow work spindle into which is fed metal bar stock or pipe so that symmetrically shaped parts can be cut as the spindle is rotated. Thus, parts such as screws, valve bodies, studs, and set screws can be turned at the output of a collet chuck. The fulcrum device is secured within the spindle of the automatic screw machine so that it will rotate and actuate the opening and closing of the collet chuck. The fulcrum device includes two chuck levers which are pivotally mounted in the fulcrum. The ends of the chuck levers are tapered so that a chuck lever sleeve which slides over the fulcrum can engage the tapered ends of the levers forcing the tapered ends of the levers to pivot toward the axis of the spindle. At the other end of each lever is a shoulder which engages a chuch lever extension which moves longitudinally a small increment in distance along the length of the spindle to engage the tapered ends of the collet so that the jaws of the collet chuck will close and clamp the workpiece.
After the workpiece is turned and cut off, a feed tube within the spindle retracts and advances the workpiece a predetermined length before the jaws of the collet chuck are closed to grip the workpiece. The collet chuck serves not only to grip the workpiece but to turn it while various tools are used to shape or form the metal on the machine.
Conventional fulcrum devices use chuck lever pins which are tapered and frictionally engage within the fulcrum device. The lever pins eventually wear so that the fulcrum has to be removed from the machine in order to drive out the tapered pins so that replacement pins can be inserted. These conventional fulcrum devices using tapered pins have been found to be difficult to maintain since the tapered pins are hard to install since the tapered hole must be hand reamed to fit the tapered pin. Upon removal, the tapered pin cannot be reused.
A device which substantially corrects these prior art shortcomings and which is currently in use in the industry is described in U.S. Pat. No. 3,915,464 to Berry issued Oct. 28, 1975. Notwithstanding the presence of such above-referred to device, there remains a need for a more positive clamping action on both ends of the Berry pin so as to insure that the pin is stationary vis-a-vis the chuck lever on which it is pivoted so as to reduce wear. It would furthermore be desirable to modify the configuration of the above referred to pin such that it is simpler, less complex to machine, and, accordingly, less costly. It would also be desirable to form such a pin of symmetrical configuration such that it may be reused in an alternate position so as to increase the wear characteristics thereof.
The present invention, accordingly, provides an assembly which accomplishes these above objectives and thus constitutes an improvement over the aforementioned fulcrum device described in the Berry patent. These and other objectives of the present invention are provided by an assembly for mounting a pivotable member such as a chuck lever from a housing such as the head of a fulcrum holder, said head including trunnion means in turn having a laterally extending bore passing therethrough for receipt of a symmetrical cylindrically shaped pivot pin in turn having a smaller diameter axial extension projecting from each end surface thereof, said housing including laterally open surfaces adjacent opposite sides of said trunnion means, said open surfaces each having an initially counterbored inwardly extending threaded bore for receipt of a headed screw, said screw heads adapted to contact said pin extensions when said screws are upwardly moved thereby positively positioning said pivot pin in said trunnion means .